1. Field of the Invention
This invention relates to headlamps for vehicles, and to light units for such headlamps; the term `light unit` is used to denote an assembly of a reflector and a lens, which, as will become clear, must be releasably held together for the present invention to be applicable.
2. The Prior Art
There have been various forms of headlamps for vehicles:
(1) The main headlamps on old vehicles and auxiliary headlamps (e.g. anti-fog or long-range headlamps) of modern vehicles comprise a shell which is mounted outside the bodywork of the vehicle, and encloses the optical system (lamp and reflector) and is formed with a large light-transmitting opening, the opening being closed by a glass lens. The lens hermetically seals the headlamps and often also has an optical diffusing effect (diffusing ribs); PA1 (2) The main headlamps on modern vehicles are fitted into recesses formed in the vehicle body. In their simplest form, these lamps comprise a reflector, usually of dished sheet-metal, having an opening covered by a lens used for sealing and, if required, for diffusion. This structure is normally called a "light unit". In some cases, an intermediate ring is disposed between the lens and reflector, in order to have a greater distance between the lens and the reflector. PA1 (3) In some vehicles, light units are mounted in special compartments or shells formed with a light-transmitting aperture closed by a lens. The compartments or shells may or may not be integral with the vehicle body.
In all cases, the lens has a main flat or slightly convex part and a peripheral mounting zone which bears against an edge of the shell or the reflector, around the front aperture thereof. In the present case, the term "shell" should be taken in its widest sense to include separate shells, reflectors, and compartments of the vehicle body.
In all existing systems, the entire optical system, including the reflector, has to be replaced if the lens breaks as a result of a local impact. The reason is that pieces of glass from the broken lens enter the headlamp and some inevitably remain there, in spite of the most careful cleaning, and rapidly damage the optical system. Another result of a broken lens is that water vapour and dust enter the reflector and rapidly damage its surface.
For obvious economic reasons, however, it would be desirable to replace only the lens, while re-using the other components, especially the reflector, which is often the most expensive part of the headlamp.
It is an object of the invention to provide a headlamp in which the reflector need not be replaced if the lens should be broken.